The local indy Volvo shop recommended replacing all four tires at the same time. car has 45k miles now. we got it at 15k with the stock tires, which were toast. we put pilot sports a/s on, which have been nice enough. now the rears are done, but the fronts are still pretty good. <p>is there any real problem with replacing only the rear tires? is there a real chance of overheating the central diff? what else could go wrong?<p>thanks!